Recently, a solid electrolytic capacitor manufactured by forming a solid electrolytic layer with a conductive polymer on a dielectric oxidation film formed on the surface of an anode body is being developed. For example, a solid electrolytic capacitor is being developed, in which a solid electrolytic layer that is formed using a conductive polymer as a solid electrolyte and a cathode body are sequentially formed on a dielectric oxidation film formed on the surface of an anode body (film-forming metals) that is composed of the porous metal bodies having a valve action, such as, aluminum, niobium, tantalum, titanium, or magnesium.
As compared with the conventional solid electrolytic capacitor that is formed using manganese dioxide as a solid electrolytic layer, the solid electrolytic capacitor that is formed using a conductive polymer as a solid electrolytic layer exhibits 10 to 100 times higher conductivity of the solid electrolyte, and also, can greatly decrease an ESR (Equivalent Series Resistance).
For this reason, it is expected that the solid electrolytic capacitor is applied for a variety of uses, such as, the absorption of high frequency noise.
A method for forming the solid electrolytic layer on the dielectric oxidation film is roughly classified into a chemical oxidative polymerization method and an electrolytic polymerization method.
In addition, pyrrole, thiophene, 3,4-ethylenedioxythiophene, or aniline is known as a monomer that constitutes a conductive polymer material.
However, for the chemical oxidative polymerization method and the electrolytic polymerization method, since a polymerization reaction is performed on a dielectric oxidation film, it might be easy to mix impurities in a solid electrolytic layer, and a short circuit might be caused.
In addition, it might be easy to complicate a manufacturing process.
As a countermeasure, a polymer suspension coating method is known as a method for forming a solid electrolytic layer on a dielectric oxidation film without performing a chemical oxidative polymerization or an electrolytic polymerization.
For example, a method including applying a dispersion including a conductive polymer on a dielectric oxidation film and then drying the dispersion is known as a method for forming a solid electrolytic layer of a conductive polymer on a dielectric oxidation film.
The dielectric oxidation film is formed on the surface of an anode body of porous metal, and thus, has a fine concave-convex shape.
For this reason, for the method for applying the dispersion including a conductive polymer on a dielectric oxidation film, it is difficult to impregnate the dispersion including a conductive polymer to the inside of the dielectric oxidation film.
As a result, it is difficult to form a solid electrolytic layer in the inside (fine pore) of the fine concave-convex shape of the dielectric oxidation film, and thus, the solid electrolytic layer is only formed on the surface layer. Therefore, there was a problem in that a capacity incidence of the solid electrolytic capacitor that can be obtained becomes low.
In addition, lately, a solid electrolytic capacitor requires reliability in all circumstances as well as high capacity as described above, and especially, humidity stability (moisture resistance) is considered as the most important thing.
Especially, it is required to inhibit the increase of an ESR (Equivalent Series Resistance) for a humidity resistance test under the hard atmosphere of 65° C. and 95% RH.
Accordingly, a method for obtaining a conductive composition with a low moisture absorption by including a specific compound in a conductive composition including a conductive polymer base been proposed (Patent Document 1).
In addition, a method for obtaining a conductive composition with a low heat deterioration due to heating by including an alkali compound in a conductive composition has been proposed (Patent Document 2).